Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Wed, 23 Aug 2006 17:00:40 -0500

Till Straumann wrote:

I know about one device that will perform 97
bus accesses inside its ISR if it gets all-1s from its read cycles.

This driver should probably be rewritten. That many VME accesses from an
ISR introduce serious latencies (even w/o bus timeouts).

Ah, but in normal operation it probably only performs 4 or 5 bus
accesses at most; the problem comes if it thinks (from erroneous all-1s
return values when reading its status registers) that it needs to do I/O
on every one of its input and output channels. This could very easily
happen if someone hot-swapped out a VME64 IPAC carrier board the device
was mounted on (which shouldn't happen since this driver is not hot-swap
safe, but it might still occur by mistake).
I agree that this is probably a bit of a straw man argument, but it
illustrates the possible consequences of the Motorola + Tundra + Marvell
design decisions on our existing software.
Anyone interested in MicroTCA to replace the now aging VMEbus?
- Andrew
--
There is considerable overlap between the intelligence
of the smartest bears and the dumbest tourists.
  -- Yosemite National Park Ranger

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System